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The details of Di-Air, a new NOx reduction system using continuous short pulse injections of hydrocarbons (HC) in front of a NOx storage and reduction (NSR) catalyst, have already been reported. This paper describes further studies into the deNOx mechanism, mainly from the standpoint of the contribution of HC and intermediates. In the process of a preliminary survey regarding HC oxidation behavior at the moment of injection, it was found that HC have unique advantages as a reductant. The addition of HC lead to the reduction or metallization of platinum group metals (PGM) while keeping the overall gas atmosphere in a lean state due to adsorbed HC. This causes local O₂ inhibition and generates reductive intermediate species such as R-NCO. Therefore, the specific benefits of HC were analyzed from the viewpoints of 1) the impact on the PGM state, 2) the characterization of intermediate species, and 3) Di-Air performance compared to other reductants.

In this study, instead of investigating NOx storage reaction improvements, the NOx adsorption phenomenon was focused on and analyzed to improve NOx trapping performance at lower temperatures. As a NOx adsorbing material, "Ag" was expected to enhance NOx adsorption and reduce the sulfur regeneration temperature due to the abundance of adsorbed oxygen and moderate basicity. However, when using this material in an actual system, we had to reduce the sulfur regeneration temperature, increase NOx adsorption capacity and improve NOx desorption further. Addition of TiO₂, working as an acidic material, was found to decrease sulfur regeneration temperature. Additionally, it increased the NOx adsorption capacity through improved Ag dispersion which plays an important role in NOx adsorbing. Consequently, a greater NOx trapping performance than NSR catalyst was achieved at lower temperatures.

We investigated filtration and oxidation behavior of secondary particle of particulate matter (PM) in the diesel particulate filter (DPF) wall using a newly developed visualization technique. The observations from magnified cross section view of the test piece cut out from full sized DPF made of Cordierite DPF and SiC. DPF. Only in the beginning of the filtration process, the PM penetrates into deep inside of the DPF wall. And in the PM forced oxidation process, the PM in the wall was oxidized first, then the PM cake layer on the DPF wall thinner by oxidized from contact part with the DPF wall. We carried out these observations with the SiC DPF. Further, we have tried to estimate the activation energy of the PM oxidation from the shrinking form of accumulated secondary particles of PM inside of the cordierite DPF loaded by platinum (Pt). We confirmed that the experimented value of the activation energy is close to that of former researchers.

One primary result of the reduction of platinum group metals (PGM) within a catalytic converter is the decline in NOx conversion efficiency. This paper hypothesizes that the primary factor of this decline to be hydrocarbon (HC) poisoning. To maintain high NOx conversion efficiency as the PGM reduces, Rh activation improvement becomes significant to overcome the HC poisoning. Analysis of the Rh deterioration mechanism found that it is effective to separately arrange Rh and CeO2 on the converter, avoiding the Rh deactivation. By this improvement, we improved the catalyst activity at less than 25% of the original Rh loading.

Conventional Three-way catalysts consist of precious metals and metal oxide supports. The sintering of precious metals is known to cause a decrease in the catalytic activity. Recently, we discovered that Pt/Ce-based oxide catalysts have high durability compared to Pt/Al2O3 following aging treatment. Using X-ray absorption analysis, we found that the Pt-O-Ce bond, that is, the Pt-support interaction, inhibits the sintering of Pt particles.